J. MolL Stud. (1996), 62,177-184 © The Malacologicat Society of London 1996

NUTRITIONAL BUDGET FOR THE GRAECA (: )

N. ELEUTHERIADIS and M. LAZARIDOU-DIMITRIADOU

Department of Zoology, School of Biology, Aristotle University, 54006 Thcssaloniki, Greece Downloaded from https://academic.oup.com/mollus/article/62/2/177/1078462 by guest on 24 September 2021 (Received 28 February 1995; accepted 6 October 1995)

ABSTRACT Dimitnadou & Daguzan, 1978; Staikou & Lazandou-Dimitriadou, 1989; Lazaridou-Dimi- The nutritional budget of Buhynia graeca (Wester- tnadou & Kattoulas, 1991). lund) was studied using samples of a snail population The freshwater prosobranch Buhynia graeca of Lake Kerkini (N Greece). A laboratory investi- (Westerlund) feeds both by radula grazing, of gation of food consumption and assimilation in B. the Aufwuchs (the largely algal 'scum' flora) or graeca was undertaken using Aufwuchs as food. On the basis of this investigation estimates of natural epilithic fouling coat and/or by ctenidial filter- consumption and assimilation efficiencies were made. feeding, on phytoplankton and other seston, as Reference is made to the energy (in terms of organic is typical of the Bithyniidae. The frequency of carbon content) invested in egg production. filter-feeding may depend on the availability of The highest daily rates of consumption, faecal other food sources and the nature of the sus- production and assimilation were observed in newly pended particles (Fretter & Graham, 1962; hatched snails and the lowest rates in mature snails. Brendelberger, 1995). The same pattern of mean ingestion and assimilation This paper arises from a general investi- rates of organic carbon (both protein and non pro- gation of the ecology and ecophysiology of tein) and of nitrogen, was observed in both sexes. prosobranch (Eleutheriadis & Lazandou-Dimi- It was assumed that this snail feeds exclusively on the Aufwuchs, which was abundant in the study area, triadou, 1995) and pulmonate snails in the and estimates of annual consumption and annual artificial Lake Kerkini in Macedonia, northern faecal production (per m2) in the field were derived Greece. It is concerned with the consumption Accordingly, the annual consumption rates were and assimilation rates of Bithynia graeca under 218 9 g dry weight of Aufwuchslm2 in females, and experimental conditions and the estimation of 227.7 g in males; similarly, the annual rates of faecal consumption, assimilation, growth and ecologi- production were 101.8 g dry wt/m2 in females and 2 cal efficiencies of this prosobranch snail in 99 2 g/m in males The assimilation efficiency for all Lake Kerkini. B. graeca is an endemic species size classes was found to be 53 5% in females and of the Greek lakes. It is dioecious and in Lake 56.4% in males. Kerkini is semelparous, with a lifespan of approximately 12 months (Eleutheriadis & Lazandou-Dimitnadou, unpublished). INTRODUCTION Ingestion and assimilation are two essential MATERIALS AND METHODS phases of energy transport from one trophic B graeca was collected from the exposed surfaces of level to another and thus they represent an the undersides of rocks which constitute the barrage important part of ecosystem functioning. Many of Lake Kerkini. A quadrat of 5 x 5 cm2 was used freshwater gastropods are primary consumers during sampling. The study began in June 1991 when and thus play an important role in matter and the snails were on average 1 month-old [shell height energy transfer from the producer level to (H) = 1.0 ± 0-3 mm; mean ± S.D.] and continued until higher trophic levels. August 1991 (H = 1.4 ± 0.8 mm) when the snails In recent years, a number of quantitative were 3 months old No experiments were possible from September 1991 to February 1992 because the studies have dealt with food consumption and snails hibernated. Subsequent experiments were per- assimilation, in both freshwater gastropods formed on the same cohort from March until May (McMahon, 1975; AJdridge, Russell-Hunter & 1992 (H =• 42 ± 0.8 mm); thus by the end of the study Buckley, 1986) and terrestrial ones (Mason, period the snails were 11 months old. Prior to each 1970a; Stern, 1968,1979; Jennings & Barkham, assay the shells were cleaned of Aufwuchs and indi- 1976; Zeifert & Shutov, 1979; Lazaridou- vidual were classified by age and sex. Age determi- 178 N. ELEUTHERIADIS & M. LAZAltlDOU-DIMITRIADOU nation was made on the basis of shell height. Sex (LW) was measured. This was done after cleaning determination was based on presence of the reddish and drying the shell with filter paper To quantify testis, which was visible through the apical whorl of the daily consumption and assimilation rates and the shell as a dark patch, in male B graeca. The 11 the growth and ecological efficiencies, the formu- month-old snails were collected in a post-breeding lae of Lazaridou-Dunitnadou & Kattoulas (1991) condition. Separate calculations were made for male and the IBP global productivity symbols listed by and female consumption and assimilation efficiencies. Petmsewicz & Macfadyen (1970), were used as The experiments were carried out in the labora- follows: tory under semi-natural conditions of lighting fol- Daily consumption rate =• C/LW lowing the natural cycles of the lake and ambient Downloaded from https://academic.oup.com/mollus/article/62/2/177/1078462 by guest on 24 September 2021 Daily faecal production rate = FU/LW temperature. Daily assimilation rate = (C-FU)/LW At the start of the study Aufwuchs was collected Assimilation efficiency »(C-FU/C)*100 from the snails' habitat and dried. The dried Auf- wuchs was used throughout the study in order to C represents the total amount of food ingested in mg overcome problems caused by seasonal variation in (it stands for the TI(= ingestion) term of Russell- Aufwuchs quality (McMahon, Douglas-Hunter and Hunter & Buckley, 1983), LW represents live weight Russell-Hunter, 1974) Changes in Aufwuchs quality in g of each snail, FU represents faecal production in may affect the ingestion rate (Calow, 1975) mg (le. egestion (NA) or food not assimilated), and In culture bowls (5 cm diameter and 1.5 cm high) C-FU represents the total amount of food assimi- were placed groups of 15, 10 or 5 snails, respectively lated in mg (or TA). Accordingly, the daily rates of of approximate ages (estimated from size) of 1 consumption, faecal production and assimilation are month, 3 months or 11 months. In the months for expressed as mg/g LW, whilst assimilation efficiency which data are given in Table 1, the numbers of is expressed as percentage. In order to determine snails used in experiments on ingestion were as ingestion and egestion rates for each experimental follows: June, 1 bowl of 15 immature snails aged 1 group, batches of food and faeces were analyzed for month; July, 1 bowl of 15 immature snails aged 2-3 total organic carbon content and for nitrogen con- months; August, 1 bowl of 10 females aged 3 months tent. These values were used to estimate protein and 1 bowl of 10 males aged 3 months; March, 1 carbdn and nonprotein carbon content The protein bowl of 5 females aged 10-11 months, 1 bowl of carbon was estimated by multiplying the nitrogen males aged 10-11 months; April, 2 bowls of 5 males values by 3.25. The nonprotein carbon was estimated aged 11 months, 1 bowl of 5 females aged 11 months; by subtraction of the protein carbon from the total May, 1 bowl of 5 males aged 11-12 months, 1 bowl organic carbon, value (Russell-Hunter & Buckley, of 5 females aged 11-12 months. The water used in 1983). Carbon analyses were earned out using the the experimental cultures was from Lake Kerkini "wet oxidation' method outlined by Russell-Hunter, and had been boiled and filtered. Carbon content Meadows, Apley & Burky (1968). Nitrogen analyses was determined for some of the snails from each of were done using the method of Elia, Steudler & these bowls and from additional bowls in early and Corwin (1977). These batch analyses provided appro- late August (Table 2). priate carbon and/or nitrogen values for eggs, food Before each experiment, snails were left in water and faeces. The weights recorded for each experi- for 24h in order to empty the gut; the ingestion rate mental group could then be used to obtain individual is reported to be relatively unchanged by starvation rates of total carbon and nitrogen ingestion (TT) and over such periods (Calow, 1975). Over a 48h period egestion (NA), and hence total carbon and nitrogen the snails were presented with a known weight of dry assimilation rates (TA) for each snail (by subtracting Aufwuchs as food. The Aufwuchs consisted of parti- the appropriate NA rate from TI). cles < 50 |ira in diameter and with a carbonnutrogen In order to find out if differences existed within ratio of 7.8:12.8 Aufwuchs of < 50 ujn particle grade and/or between experimental groups, analysis of was used in order to facilitate the separation of variance (ANOVA) and Fisher LSD tests (following faecal material from the uneaten food (the faecal Zar, 1984) were executed, respectively. Data were pellets had a diameter > 50 uxn). logarithmically transformed prior to analysis. Imma- At the end of 48h the snails were removed. Any ture and mature snails were treated separately. uneaten food and faeces were collected from each culture bowl, and then dried and reweighed. All weights were determined, after drying to a constant RESULTS weight at 60 °C, using a Sauter AR 1014 micro- balance (precision ± 0.001 g). The highest value for daily consumption rate To enable calculation of (weight-specific) snail- was observed in newly hatched snails in June carbon and-nitrogen content, from three to seven (432 mg/g LW) (Fig. 1, Table 1). The lowest snails were separately decalcified in 8.5% HNOj, and the periostracum removed, before drying and weigh- value for daily consumption rate was observed ing. All the data (in terms of organic carbon and in mature snails with shell height 4.8 mm in nitrogen content) are expressed in ug/mg. May 1992 (102 mg/g LW for female snails and For the estimation of daily consumption, faecal 147 mg/g LW for male snails (Fig. 1, Table 1). production and assimilation rates, the live weight Values of daily faecal production rate followed NUTRITIONAL BUDGET FOR BITHYNIA GRAECA 179

(mgVtiva weight (g) carbon ingestion rate, with the next lowest 500: value occurring in July 1991 (Fig. 2D). females 400- The assimilation efficiency (Table 1) fluctu- 300: 2oo: ated between 50% and 61%, the highest value ioo: (61%) was achieved by male snails in August (with 58% for females). In newly hatched Jun JuL Aug. Apr May 1991 1992 snails (ie. in June 1991) the assimilation effi- (mgVVvs weight (g) ciency was 60% (data for males and females

500- Downloaded from https://academic.oup.com/mollus/article/62/2/177/1078462 by guest on 24 September 2021 males pooled). 400- 300" A statistically significant monthly variation 2O0- in the carbon content of whole snails was 100" detected between June 1991 and May 1992

Jun j Aug. M*r Apr May (F,46 = 10.07, P = 0.0003 for immature snails 1991 Months 1992 and F3Jo = 1838, P = 0.0001 for mature snails; Figure L Mean ingestion and assimilation rates per see Table 2). Comparisons between the dif- day per g body wet weight of Buhynia graeca fed on ferent months indicated the following: a non- Aufivuchs from hatching to maturity (with open significant increase from June to July 1991, a symbols the ingestion and with solid ones the assimi- significant decrease in the carbon content of lation) mature snails in August 1991 preceding hiber- nation (F, = 0.128; P < 0.05), and a significant increase, in the period leading up to copula- the general pattern of daily consumption rate tion, between late August 1991 and April 1992 (Fig. 1, Table 1). (F6 = 0, 154, P < 0.05 for immature snails, and The maximum ingestion rate for carbon (9.3 F13 = 0.099, P < 0.05 for mature snails). ug/hour/mg tissue dry wt) was observed in The values for carbon content of tissue newly hatched snails in June and the lowest (excluding shell) followed the same pattern as (2.21 for female snails and 3.53 for male snails) that for the whole in immature snails in May in mature snails (Fig 2A). Values of (Table 2), but without the increase between mean assimilation rates (ug carbon/hour/mg June and July 1991. As for mature snails, the tissue dry wt) followed the general pattern of values for carbon content of tissue (excluding mean ingestion rate (Fig. 2A). The same pat- shell) followed the same pattern as that for the tern was observed in the mean ingestion rate whole animal except between early August to for nitrogen (ug/hour/mg tissue dry wt); the late August 1991. With respect to shell carbon highest value (0.87) was also recorded in newly content, the value recorded for May (1992) hatched snails in June and the lowest (0.24 for was significantly less than those recorded for female snails and 038 for male snails) in the other 3 experiments (F33 = 5.55; P < 0.05); mature snails in May (Fig. 2B). Values of mean no other significant differences were detected. assimilation rate for nitrogen followed the By multiplying the number of eggs laid by same pattern as the corresponding values for each snail (109 ± 19.05, n = 8) by the egg mean ingestion rate (Fig. 2B). The highest carbon content (Table 3) it was possible to value (2.83) for the mean ingestion rate of calculate the carbon spent on egg production, protein carbon was also observed in newly and hence to determine the nutritional budget hatched snails in June, and the lowest (0.78 for of an individual B. graeca during its lifetime female snails and 1.23 for male snails) in (Table 4). mature snails in May (Fig. 2C). Values of mean assimilation rate of protein carbon followed The direct ratio of effort ((carbon output in the same pattern as the corresponding values the form of gametes to carbon input from for mean ingestion rate (Fig. 2C). Finally, the food) x 100) was 13.8% for female snails. The highest value (6.47) for the mean ingestion values of carbon content of the snails dry body rate of nonprotein carbon was recorded in tissue before and after the reproductive period newly hatched snails in June, with the lowest were 710 and 778 |ig carbon respectively (April value (1.43 for females and 2.3 for males) again 92 and May 92). From the mean number of /m2, data occurring in mature snails in May (Fig. 2D). 2 Values for mean assimilation rate of nonpro- for all size classes pooled (ie. 12172 snails/m ) tein carbon showed a maximum in June 1991 (Eleutheriadis & Lazaridou-Dimitriadou, in and a minimum in May 1992, thus following prep.), and the daily amount of food consumed the same pattern as those for the nonprotein by them per month, it was possible to deter- mine the annual consumption and the annual Downloaded from https://academic.oup.com/mollus/article/62/2/177/1078462 by guest on 24 September 2021

Table 1. Monthly rates and efficiencies for the principal parameters of individual nutritional budget of Bithynia graeca fed on Aufwuchs from hatching to maturity (June 1991 to May 1992) See Materials and Methods for the numbers of snails used in the experiments.

June July August March April May

Daily consumption 432 404 female 238 female 285.7 female 295.0 102 0 female m male 228 male 220.8 male 297.0 male 147.5 m Daily faecal production rate (mg dry/g live) 173 194 female 88 female 137.1 female 143.5 female 51.0 male 80 male 91.3 male 145.0 male 73.7 Daily assimilation rate (C-F)/g live 259 207 female 150 female 148.6 female 151.5 female 51.0 2 male 148 male 129.1 male 152.0 male 73.7 Monthly ingestion mg 17.3 29.1 female 17.9 female 50 female 109 female 60 6 55 male 14.9 male 53 male 110 male 72.0 Monthly assimilation mg 10.4 15 5 female 10.4 female 26 female 55.5 female 30.3 2 male 9.1 male 31 male 56.0 male 36.0 Monthly ingestion ug Carbon 1138.5 1377 female 1395.5 female 3150 female 6850 female 3851 male 1162.2 male 3340 male 6905 male 4536 6 Monthly assimilation ug Carbon 655.5 497.4 female 727.7 female 1330 female 3123 female 1697 o male 660.6 male 1800 male 3203 male 2016 c Assimilation efficiency % 60 0% 52.0% female 58.0% female 52.0% female 51.0% female 50 0% 6 male 61.2% male 58 5% male 510% male 50.0% 2

Tissue dry weight (mg) 0.17 0.45 female 0.6 female 0.9 female 1.7 female 24 O male 0.6 male 1.1 male 1 8 male 2.1 O Shell dry weight (mg) 0 25 0.66 female 1.1 female 1.8 female 3.4 female 4.9 c male 1.1 male 2.2 male 34 male 4.2 NUTRITIONAL BUDGET FOR BITHYSIA GRAECA 181

101 8: CO 6: i* 4" %l r Jun. Jul. AugT' Mar. Apr. May Jun. Jul.Aug^ Mar. Apr. May o if males 5.$ males Downloaded from https://academic.oup.com/mollus/article/62/2/177/1078462 by guest on 24 September 2021

Jun. Jul. Aug. Mar. Apr May Jun. Jul. Aug. Mar. Apr. May 1991 1992 1991 1992

0.8- o.e T3 1£3• 0 o3 *- ^ 02 « »3- nu is o.o Jun. Jul. Aug. Mar. Apr. May Jun. Jul. Aug." Mar. Apr. May g1.0 males |l| 1§2 0.8 c E g> g- males 0.6" 3.0 Z 4" 0.4- 0.2" 2 0.0 0 Jun. Jul. Aug. Mar. Apr. May Jun Jul. Aug."Mar. Apr. May 1991 1992 1991 1992 Months Months Figure 2. Mean ingestion (D) and assimilation (•) rates of A. ug carbon. B ug nitrogen, C. ug protein carbon, and D. ug nonprotein carbon per hour per mg tissue dry weight of Bithyma graeca females and males fed on Aufwuchs from hatching to maturity. faecal production per square metre in the field. carbon and nonprotein carbon. The differences It was assumed that the animals fed exclusively observed between immature and mature snails on the Aufwuchs (which was abundant in the might be due to a decrease in metabolic rate study area). Accordingly, estimates for annual with age. A similar pattern has been noted for consumption of 218.9 g dry weight of Auf- B. graeca with respect to the assimilation wuchslm2 for females, and 227.7 g dry weight efficiencies for total carbon, nitrogen, protein of Aufwuchslm2 for males, were derived. The carbon and non protein carbon, and for gross corresponding annual rates of faecal produc- and net growth efficiency for carbon at 26 °C tion would be 101.8 g dry weight/m2 for the (Eleutheriadis & Lazaridou-Dimitriadou, 1995). females and 99.2 for the males. The assimi- The same decrease in metabolic rate with lation efficiency for all size classes was esti- maturity has been reported for other fresh- mated at 53.5% for the females and 56.4% for water gastropods (Aldridge et al, 1986) and the males. for terrestrial species (Stern, 1968; Jennings & Barkham, 1976; Lazaridou-Dimitriadou & Daguzan, 1978; Zeifert & Shutov, 1979; DISCUSSION Staikou & Lazaridou-Dimitriadou, 1989; Lazaridou-Dimitriadou & Kattoulas, 1991). The highest daily rates of consumption, faecal The above parameters relating to the indi- production, and assimilation were observed in vidual nutritional budget of the snails are also newly hatched snails, and the lowest values in influenced by the time of year and the physio- older snails. Similar patterns were observed in logical state of the animals. The high values of both sexes for the mean ingestion and assimi- daily consumption rate and daily faecal lation rates for (total) carbon, nitrogen, protein production rate in March and April are related 182 N ELEUTHERIADIS & M. LAZAR1DOU-DIMTTRIADOU to rapid growth after hibernation and to prepa- to to rations for the reproductive period. Similar 44 results have been reported for terrestrial co snails; for example, Stem (1968, 1979) for CD £ — Anon rufus and A. laevis, Lazaridou-Dimitri- 3 >~ adou & Daguzan (1978) for Euparypha pisana, Charrier & Daguzan (1980) for Helix aspena, Staikou & Lazaridou-Dimitriadou (1989) for o M Helix lucorum and Lazaridou-Dimitriadou & tN CN m Kattoulas (1991) for Eobania vermiculata. Sig- Downloaded from https://academic.oup.com/mollus/article/62/2/177/1078462 by guest on 24 September 2021 44 cn

oo period). Such differences may be due to ana-

•H in H bolic expenditures related to egg production in

44 § the females and to kinetic energy expenditures involved in extensive gene dispersal in the a males (Russell-Hunter & Buckley, 1983). The 3 f* co co ^ r** CD co 3 PO c .3 decreases in daily consumption and faecal pro- o I .= i .= 11 .i 1 11 duction rate and in monthly ingestion rate CD observed in August are probably due to the £ fact that snails were less active as a result of 3 CO 44 CO 44 increased ambient temperature. However, the C 44 44 CN CO I cn high values observed in assimilation efficiency r*. 44 C CD in August are probably related to the accumu- 10 0 CD r* 18 5 3 CN CN CD CD CD lation of food reserves prior to hibernation. cn 3 CO CO CO 3 CO CD CO B I The above was also noted, for H. lucorum, a CD E • OS • E I CO — — .is E c terrestrial snail found in Greece, by Staikou & Lazaridou-Dimitriadou (1989) and for E. o LD s vermiculata. by Lazandou-Dimitriadou & 44 44 Kattoulas (1991). CO I CN ^t CN CD The values of assimilation efficiency in B. CD CD C 3 3 3 graeca are lower than those reported for other E a prosobranch gastropods (ie. 70% to 95%; o sE a E g E E Russell-Hunter & Buckley, 1983). McMahon et al. (1974), McMahon (1975) and Aldridge etal. (1986) suggested that food quality is probably 00 CD responsible for low efficiencies. "~ 44 44 10 in The monthly rates showed an increase of CT> CN 118% in ingestion and 135% in assimilation •£ s CD 8 3 3 between March and April (Table 1); this was CD CO probably a result of energy expenditure on

"o Ul l • Ul | • c c growth and egg production. In contrast, a CD decrease in ingestion rate of 43.5% and a simi- c o lar decrease of 45.5% in assimilation (Table 1) u cCD CD 1 was recorded between April and May, presum- nt ) ably because following the end of the breeding "O 5> 3 = JO CD period the animals expend very little energy on "1 "5 II ) growth. The direct ratio of effort of 13.8% •o "o dr y tis s •s (energy invested in reproduction relative to c c a c CO c CD o CD somatic growth) is similar to that reported for E S E Sc E 0 other semelparous freshwater gastropods. 22% u

Aufwuchs 58.2 * 13 (n- 16) 6.2 ± 0.3 (n-16) Whole animal 103±30(n»130) 20 ± 3.5 (n - 70)

Shell 22.7±8(n = 12) 2.5 ± 0.2 (n - 5) Downloaded from https://academic.oup.com/mollus/article/62/2/177/1078462 by guest on 24 September 2021 Eggs (value/egg) 10 ±0.4 1 ±0.1 n =• 3 (egg capsules) n - 3 (egg capules)

Table 4. The principal parameters of the nutritional budget of Bithynia graeca during its lifetime (12 months).

In 12 months In 12 months In 1 day In 1 day (mg) (mg carbon) (mg) (mg carbon) Ingestion female 258.9 female 17709 female 0.71 female 48.51 male 269.8 male 18447 male 0.74 male 50.54 Assimilation female 135.0 female 7874 female 0 39 female 21.57 male 142.5 male 7993 male 0.39 male 21.90 Carbon spent on egg production 1090

lata and 35% for Helisoma tnvolvis (see Calow, rum (2.6 g/m2/year fed on Petasites or 3.54 1978,1979). g/m2/year if fed on Urtica), and by Lazaridou- There is an increase in the carbon content of Dimitnadou & Kattoulas (1991) for E. vermicu- the snail's body after the reproductive penod lata (11.5 g/m2/year fed on Urtica). These (April, 710 u.g carbon, and May, 778 |ig car- differences may be due to the higher density of bon), although 136 ug were utilized during the B. graeca in Lake Kerkini (12172 snails/m2/ first stage of egg production; this increase year, Eleuthenadis & Lazandou-Dimitriadou, shows that the energy expended on egg pro- unpublished) compared with those of the duction comes from concurrent trophic input. terrestrial species and/or to the different food A high reproductive output (82.2%) achieved consumed by aquatic snails. The diet of most through trophic input was also described by freshwater gastropods is composed of algae Russell-Hunter, Apley & Hunter (in Russell- and detritus, which is not as heavily sclerotized Hunter & Buckley, 1983) for Melampus sp as is the diet of terrestrial species (leaf litter or The yearly consumption (of Aufwuchs) per other plants) and so is more refractory to m2 in B. graeca exceeds those values reported digestion. for terrestrial gastropods: 2.8 g/mz/year was recorded for a number of snail species fed on beech litter (Mason, 1970b); 8.17 g/m2/year for ACKNOWLEDGEMENTS Arion ater fed on leaf litter (Jennings & Barkham, 1976), 23 g/m2/year for Bradybaena We thank S.W. Attwood for helpful comments fruticum (see Zeifert & Shutov, 1979); 6.8 on our manuscript. g/m2/year for H. lucorum fed on Petasites, or 15.81 g/m2/year if fed on Urtica (sec Staikou & Lazaridou-Dimitriadou, 1989); and 23.9 g/m2/ REFERENCES year for E. vermiculata fed on Urtica (see Lazandou-Dimitriadou & Kattoulas, 1991). ALDRIDGE, D W., RUSSELL-HUNTER, W.D.